Microstructure and mechanical properties of electron beam weld joints of a Zr41Ti14Cu12Ni10Be23 bulk metallic glass with Zr

The electron beam welding technique was used to join Zr41Ti14Cu12Ni10Be23 bulk metallic glass (BMG) to crystalline pure Zr. Compositional, microstructural, and mechanical property variations across the welded interface were evaluated. It is shown that a crystalline layer develops close to the welding interface. Transmission electron microscopy of this layer indicates the crystalline phase to be tetragonal with lattice parameters close to that reported for Zr2Ni. However, the composition of this phase is different as it contains other alloying additions. The interface layer close to the bulk metallic glass side contains nanocrystalline Zr2Cu phase embedded in the glassy matrix. Nanoindentation experiments indicate that the hardness of the crystalline layer, although less than the bulk metallic glass, is more than the Zr itself. Commensurately, tensile tests indicate that the failure of the welded samples occurs at the Zr side rather than at the weld joint.

Effect of Dilatation on the Elasto-Plastic Response of Bulk Metallic Glasses Under Indentation

Elasto-plastic response of bulk metallic glasses (BMGs) follows closely the response of granular materials through pressure dependent (or normal stress) yield locus and shear stress induced material dilatation. On a micro-structural level, material dilatation is responsible for stress softening and formation of localized shear band, however its influence on the macro-scale flow and deformation is largely unknown. In this work, we systematically analyze the effect of material dilatation on the gross indentation response of Zr-based BMG via finite element simulation. The strengthening/softening effect on the load-depth response and corresponding stress-strain profiles are presented in light of differences in elastic-plastic regimes under common indenters. Through comparison with existing experimental results, we draw conclusions regarding selection of suitable dilatation parameters for accurately predicting the gross response of BMGs

Dynamic and thermodynamic anomalies of water at low temperatures: from bulk water to reverse micelles and DNA hydration layer

Liquid water is known to exhibit remarkable thermodynamic and dynamic anomalies, ranging from solvation properties in supercritical state to an apparent divergence of the linear response functions at a low temperature. Anomalies in various dynamic properties of water have also been observed in the hydration layer of proteins, DNA grooves and inside the nanocavity, such as reverse micelles and nanotubes. Here we report studies on the molecular origin of these anomalies in supercooled water, in the grooves of DNA double helix and reverse micelles. The anomalies have been discussed in terms of growing correlation length and intermittent population fluctuation of 4- and 5-coordinated species. We establish correlation between thermodynamic response functions and mean squared species number fluctuation. Lifetime analysis of 4- and 5-coordinated species reveals interesting differences between the role of the two species in supercooled and constrained water. The nature and manifestations of the apparent and much discussed liquid-liquid transition under confinement are found to be markedly different from that in the bulk. We find an interesting `faster than bulk' relaxation in reverse micelles which we attribute to frustration effects created by competition between the correlations imposed by surface interactions and that imposed by hydrogen bond network of water.

Temperature dependence of the energy gap and free carrier absorption in bulk InAs0.05Sb0.95 single crystals

Temperature dependence of the energy gap and free carrier absorption in a high-quality InAs0.05Sb0.95 single crystal was studied between 90 K and 430 K through the absorption spectra. At this alloy concentration, the room-temperature energy gap was measured to be 0.15 eV. Varshni- and the Bose–Einstein-type fit parameters were obtained from the measured temperature dependence of the energy gap, and the latter gave the zero-temperature gap to be 0.214 eV. It was found that although Weider’s empirical formula for the dependence of the energy gap on temperature and the alloy concentration agrees with the value of the gap at room temperature, it is inaccurate in describing its temperature dependence. From the free carrier absorption measurements, the phonon limited cross section of 7.35×10−16 cm2 at 15 μm was deduced at room temperature.

Structural, optical, and electrical properties of bulk single crystals of InAsxSb(1-x) grown by rotatory Bridgman method

Radially-homogeneous and single-phase InAsxSb(1−x) crystals, up to 5.0 at. % As concentration, have been grown using the rotatory Bridgman method. Single crystallinity has been confirmed by x-ray and electron diffraction studies. Infrared transmission spectra show a continuous decrease in optical energy gap with the increase of arsenic content in InSb. The measured values of mobility and carrier density at room temperature (for x = .05) are 5.6×104 cm2/V s and 2.04×1016 cm−3, respectively.

Evidence for a thermally reversing window in bulk Ge–Te–Si glasses revealed by alternating differential scanning calorimetry

Experiments on Ge15Te85− x Si x glasses (2 ≤ x ≤ 12) using alternating differential scanning calorimetry (ADSC) indicate that these glasses exhibit one glass transition and two crystallization reactions upon heating. The glass transition temperature has been found to increase almost linearly with silicon content, in the entire composition tie-line. The first crystallization temperature (T c1) exhibits an increase with silicon content for x < 5; T c1 remains almost a constant in the composition range 5 < x ≤ 10 and it increases comparatively more sharply with silicon content thereafter. The specific heat change (ΔC p) is found to decrease with an increase in silicon content, exhibiting a minimum at x = 5 (average coordination number, r = 2.4); a continuous increase is seen in ΔC p with silicon concentration above x = 5. The effects seen in the variation with composition of T c1 and ΔC p at x = 5, are the specific signatures of the mean-field stiffness threshold at r = 2.4. Furthermore, a broad trough is seen in the enthalpy change (ΔH NR), which is indicative of a thermally reversing window in Ge15Te85− x Si x glasses in the composition range 2 ≤ x ≤ 6 (2.34 ≤ r ≤ 2.42).

XPS and x-ray absorption-edge studies of the surface and bulk valence states of cerium in ceco2

XPS and LIII X-ray absorption edge studies regarding the valence state of cerium have been carried out on the intermetallic compounds CeCo2, which becomes superconducting at low temperatures. It is observed from XPS that the surface shows both Ce3+ and Ce4+ valence states, while the X-ray absorption edge studies reveal only Ce4+ in the bulk. Thus valence fluctuation and superconductivity do not coexist in the bulk of this compound.

The electrical switching and thermal behavior of bulk Ge(15)Te(85-x)Sn(x) and Ge(17)Te(83-x)Sn(x) glasses

Bulk Ge(15)Te(85 - x)Sn(x) and Ge(17)Te(83 - x)Sn(x) glasses, are found to exhibit memory type electrical switching. The switching voltages (V(t)) and thermal stability of Ge(15)Te(85 - x)Sn(x) and Ge(17)Te(83 - x)Sn(x) glasses are found to decrease with Sn content. The composition dependence of v, has been understood on the basis of the decrease in the OFF state resistance and thermal stability of these glasses with tin addition. X-ray diffraction studies reveal that no elemental Sn or Sn compounds with Te or Ge are present in thermally crystallized Ge-Te-Sn samples. This indicates that Sn atoms do not interact with the host matrix and form a phase separated network of its own, which remains in the parent glass matrix as an inclusion. Consequently, there is no enhancement of network connectivity and rigidity. The thickness dependence of switching voltages of Ge(15)Te(85 - x)Sn(x) and Ge(17)Te(83 - x)Sn(x) glasses is found to be linear, in agreement with the memory switching behavior shown by these glasses. (C) 2011 Elsevier B.V. All rights reserved.

Transport, optical and magnetotransport properties of hetero-epitaxial InAsxSb1−x/GaAs(x0.06) and bulk View the MathML source crystals: experiment and theoretical analysis

We briefly review the growth and structural properties of View the MathML source bulk single crystals and View the MathML source epitaxial films grown on semi-insulating GaAs substrates. Temperature-dependent transport measurements on these samples are then correlated with the information obtained from structural (XRD, TEM, SEM) and optical (FTIR absorption) investigations. The temperature dependence of mobility and the Hall coefficient are theoretically modelled by exactly solving the linearized Boltzmann transport equation by inversion of the collision matrix and the relative role of various scattering mechanisms in limiting the low temperature and View the MathML source mobility is estimated. Finally, the first observation of Shubnikov oscillations in InAsSb is discussed.

Decoupling of diffusion from viscosity: Difference scenario for translational and rotational motions

Recent experiments have indicated a dramatically different viscosity dependence of the translational and the rotational diffusion coefficients in a supercooled liquid as the glass transition temperature is approached from above. While the translational motion seems to be decoupled from the rising viscosity (eta), the rotational motion seems to remain firmly coupled to eta. In order to understand the microscopic origin of this behavior, we have carried nut detailed theoretical calculations of both the quantities by using a self-consistent mode-coupling theory (MCT). it is found that when the size of the solute is same as that of the solvent molecules, the conventional MCT fails to predict the observed decoupling. The solvent inhomogeneity is found to play a decisive role in determining the decoupling. The difference in the viscosity dependence between rotation and translational diffusion coefficient is discussed.

Nanoindentation response of an ion irradiated Zr-based bulk metallic glass

Nanoindentation experiments were conducted on a Ni+ ion-irradiated Zr-based bulk metallic glass (BMG). The irradiation was carried out using 2.5, 5, 10 and 15 MeV ions and a flux of similar to 10(16) ions/cm(2). Post mortem imaging of the indents reveals a transition in the deformation mechanism of the irradiated regions from heterogeneous shear banding to homogeneous flow. Additionally, the load-displacement curves exhibit a transition from serrated to continuous flow with increasing severity of irradiation damage. The stress-strain response obtained from micro-pillar compression experiments complements the indentation response exhibiting a decrease in the flow stress and an `apparent' strain hardening at the lowest irradiation damage investigated, which is not observed in the as-cast alloy. (C) 2011 Elsevier B.V. All rights reserved.